Internal combustion engine with secondary air pump for catalyst

ABSTRACT

A secondary air pump for a small internal combustion engine for supplying secondary air to the exhaust system of the engine upstream of a catalyst element. The air pump includes a thinly-profiled pump housing attached to the crankcase of the engine, an inlet in fluid communication with the atmosphere, and an outlet in fluid communication with the exhaust system of the engine upstream of the catalyst element. First and second impellers within the pump housing and are driven by the crankshaft and camshaft of the engine, respectively, and cooperate with one another and with the pump housing to define a plurality of moving working spaces which convey air from the inlet to the outlet during running of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to small internal combustion engines of the type used with lawnmowers, lawn and garden tractors, other utility implements, or with sport vehicles, for example. In particular, the present invention relates to an air pump for supplying secondary air to an exhaust system of the engine upstream of a catalyst element to facilitate operation of the catalyst element.

2. Description of the Related Art

The exhaust systems of small internal combustion engines include mufflers for reducing the noise of the exhaust output from the combustion chamber(s) of the engines. The exhaust systems include an exhaust passage connecting the combustion chamber to the muffler, wherein the muffler is either mounted directly to the engine, or is located remote from the engine and is connected to the engine by an exhaust pipe. Within the muffler, the pressure waves associated with the exhaust gases are dampened before the exhaust gases are vented to the atmosphere in order to reduce noise.

Additionally, some exhaust systems of small internal combustion engines also include a catalyst element for oxidizing components of the exhaust gas, such as unburnt hydrocarbons. The catalyst element requires a supply of atmospheric air including oxygen, referred to as “secondary air”, in order to carry out the oxidation reaction. The secondary air is typically supplied to the catalyst element via a venturi-type device associated with either the exhaust passage or muffler, wherein secondary air is drawn into the stream of exhaust gas from the atmosphere. Alternatively, an air pump driven from the engine supplies a stream of secondary air from the atmosphere to the exhaust passage or muffler upstream of the catalyst.

A problem with the foregoing methods of supplying secondary air to the catalyst is that venturi-type devices associated with the exhaust passage or muffler may not be effective for drawing a sufficient quantity of secondary air into the exhaust gas stream. Further, many air pumps which are typically used to supply secondary air to the catalyst element, such as diaphragm-type pumps, often are not powerful enough to supply a robust stream of secondary air to the exhaust gas stream and additionally, tend to take up additional space around the engine. Finally, other types of air pumps may reduce the overall power output of the engine.

What is needed is a secondary air pump for the exhaust system of an engine which is an improvement over the foregoing.

SUMMARY OF THE INVENTION

The present invention provides a secondary air pump for a small internal combustion engine for supplying secondary air to the exhaust system of the engine upstream of a catalyst element. The air pump includes a thinly-profiled pump housing attached to the crankcase of the engine, an inlet in fluid communication with the atmosphere, and an outlet in fluid communication with the exhaust system of the engine upstream of the catalyst element. First and second impellers within the pump housing and are driven by the crankshaft and camshaft of the engine, respectively, and cooperate with one another and with the pump housing to define a plurality of moving working spaces which convey air from the inlet to the outlet during running of the engine.

In one embodiment, the first impeller is driven by the crankshaft and includes a pair of lobes, and a second impeller is driven from the camshaft and includes four lobes. The lobes of the first and second impellers do not directly engage the pump housing or one another, but rather are disposed in close cooperation with the pump housing and with one another to define a plurality of moving working spaces within the pump housing. Therefore, operation of the air pump does not create friction between the moving parts of the air pump which could otherwise reduce the power output of the engine.

Additionally, in one embodiment, the air pump includes a housing body and a cover, the housing body attached to the crankcase of the engine via a plurality of fasteners, and the cover attached to the housing body via a plurality of fasteners to enclose the air pump. The housing body and cover each have a thin profile, allowing the air pump to be positioned with the a space between the crankcase and a flywheel which is mounted to an end of the crankshaft extending externally of the crankcase. Ends of the crankshaft and camshaft which extend externally of the crankcase project directly into the air pump housing, and the first and second lobes are drivingly connected to the foregoing shafts. In this manner, the air pump has a compact construction which does not increase the overall size or profile of the engine.

In one form thereof, the present invention provides an internal combustion engine, including an engine housing; first and second shafts rotatably supported by the engine housing; and an air pump, including a pump housing; an inlet in fluid communication with the atmosphere; an outlet in fluid communication with an exhaust system of the engine; first and second impellers disposed within the pump housing and driven respectively by the first and second shafts, the impellers cooperating with one another and with the pump housing to define a plurality of moving working spaces which convey air from the inlet to the outlet upon rotation of the first and second impellers.

In another form thereof, the present invention provides an internal combustion engine, including an engine housing; a crankshaft rotatably supported by the engine housing; an additional shaft driven from the crankshaft and rotatably supported by the engine housing; an exhaust system including an exhaust passage and a catalyst element; and an air pump, including a pump housing including an inlet in fluid communication with the atmosphere and an outlet in fluid communication with the exhaust passage at a location upstream of the catalyst element; and first and second impellers disposed within the pump housing and driven respectively by the crankshaft and the additional shaft, the impellers each including a plurality of lobes in meshing cooperation with one another to define moving working spaces which convey air from the inlet to the outlet upon rotation of the first and second impellers.

In a further form thereof, the present invention provides an internal combustion engine, including an engine housing; first and second shafts rotatably supported by the engine housing; and an air pump, including a pump housing; an inlet in fluid communication with the atmosphere; an outlet in fluid communication with an exhaust system of the engine; and means within the pump housing for conveying air from the inlet to the outlet upon rotation of the first and second shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of portions of an internal combustion engine including a secondary air pump in accordance with the present invention;

FIG. 2 is a perspective view of the engine portions of FIG. 1, showing components of the secondary air pump in exploded view, viewed from above;

FIG. 3 is a perspective view of the engine portions of FIG. 1, showing components of the secondary air pump in exploded view, viewed from below;

FIG. 4 is a top view of the impellers of the air pump shown in an arbitrary position within a pump cycle thereof;

FIG. 5 is a continuation of FIG. 4, showing the impellers in an advanced position from that of FIG. 4;

FIG. 6 is a continuation of FIG. 5, showing the impellers in an advanced position from that of FIG. 5;

FIG. 7 is a continuation of FIG. 6, showing the impellers in an advanced position from that of FIG. 6;

FIG. 8 is a continuation of FIG. 7, showing the impellers in an advanced position from that of FIG. 7;

FIG. 9 is a continuation of FIG. 8, showing the impellers in an advanced position from that of FIG. 8; and

FIG. 10 is a continuation of FIG. 9, showing the impellers in an advanced position from that of FIG. 9.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention any manner.

DETAILED DESCRIPTION

Referring first to FIGS. 1-3, a small internal combustion engine 20 is shown which includes an exhaust system and a secondary air pump in accordance with the present invention. Certain conventional components of engine 20, such as a crankcase cover or mounting flange, a flywheel, and a blower housing, for example, are not shown in FIGS. 1-3 in order to better illustrate the features of the secondary air pump; however, these and other conventional engine components are shown in similar engines disclosed in U.S. Pat. Nos. 6,295,959, 6,499,453, 6,612,275, 6,904,883, and 6,941,914, each assigned to the assignee of the present invention, the disclosures of which are expressly incorporated herein by reference.

Engine 20 includes an engine housing having a crankcase 22 and a cylinder block 24 integrally formed as a single component, and a mounting flange or a crankcase cover (not shown) is attached to the open lower end of crankcase 22 (FIG. 3). An upper end of crankshaft 26 is rotatably journalled in an upper bearing 28 (FIG. 2) in upper wall 30 of crankcase 22 and extends externally of crankcase 22. A flywheel/blower (not shown) is secured to the upper end of crankshaft 26 which extends externally of crankcase 22, and a blower housing (not shown) covers the upper portion of engine 20 for directing cooling air from the flywheel/blower over engine 20. A lower end of crankshaft 26 is rotatably journalled in a lower bearing (not shown) in the mounting flange or crankcase cover, and a driven component (not shown) is attached to a portion of the lower crankshaft end which extends externally of crankcase 22. Although engine 20 is shown in FIGS. 1-3 as a single cylinder, vertical crankshaft engine, the secondary air pump of the present invention may also be used in multiple cylinder and/or horizontal crankshaft engines.

Crankshaft 26 is rotationally driven by a piston slidably disposed in a cylinder bore of the engine, which is attached to crankshaft 26 via a connecting rod (not shown). Camshaft 32 includes an upper end rotatably journalled in upper camshaft bearing in upper wall 30 of crankcase 22, and a lower end rotatably journalled in a bearing (not shown) in the crankcase cover or mounting flange. As shown in FIG. 3, camshaft 32 includes cam gear 34 driven from drive gear 35 of crankshaft 26, such that camshaft 32 is driven at one-half crankshaft speed. Engine 20 additionally includes an L-head type drive train driven from camshaft 32, wherein a pair of lobes (not shown) on camshaft 32 directly actuate intake and exhaust valves (not shown) within cylinder block 24 of engine 20.

Cylinder block 24 includes an intake port 36 through which a combustion mixture is supplied to the combustion chamber of engine 20 from an air filter and carburetor (not shown), as well as an exhaust port 38 from which exhaust gases are expelled from the combustion chamber of engine 20. Cylinder block 24 additionally includes a rectangular access opening 40 for assembling and/or accessing components of the valve train, and a pair of support posts 42 integrally formed with cylinder block 24 for supporting the ignition module (not shown) of the engine.

The exhaust system of engine 20 includes muffler 44 attached directly to exhaust port 38 of cylinder block 24 via suitable fasteners, wherein exhaust port 38 and muffler 44 together define an exhaust passage extending from the combustion chamber of engine 20 to the atmosphere. Muffler 44 includes inner shell 46 and outer shell 48 each made of stamped metal, for example, which are secured to one another to define an interior volume of muffler 44 including suitable structure for dampening exhaust pressure waves. Outer shell 48 includes an outlet in the form of a plurality of holes 50 for venting exhaust gases to the atmosphere. Muffler may include one or more features of the muffler disclosed in U.S. patent application Ser. No. 10/823,322, entitled TUNED MUFFLER FOR SMALL INTERNAL COMBUSTION ENGINES, filed on Apr. 13, 2004 (Attorney Docket Ref.: TEL0666-01), the disclosure of which is expressly incorporated herein by reference. A catalyst element (not shown) is disposed within muffler 44, through which exhaust gases pass. In operation, the catalyst element oxidizes unburnt hydrocarbons within the exhaust stream before same is discharged from muffler 44. The exhaust system of engine 20 additionally includes a secondary air pump 52, as described below.

Referring to FIGS. 1-3, secondary air pump 52 generally includes pump housing 54 and cover 56. Pump housing 54 has a thin profile, and includes overlapping larger and smaller circular chambers 58 and 60 (FIGS. 1 and 2), and first and second spacer portions 62 and 64 (FIG. 3) projecting therefrom. Pump housing 54 is secured to upper wall 30 of crankcase 22 of engine 20 via suitable fasteners (not shown) or by welding, for example. Alternatively, pump housing 54 may be integrally cast with crankcase 22. Pump housing 54 additionally includes first and second apertures 66 and 68 (FIG. 2), with first aperture 66 being relatively large and fitting around upper bearing 28 of crankcase 22. The upper end of crankshaft 26 projects through aperture 66 and a corresponding aperture 70 in cover 56. The upper end of camshaft 32 projects through aperture 68 in pump housing 54. Cover 56 is a thin, plate-like element secured to pump housing 54 via at least three fasteners 73 (FIG. 2) which extend through holes 72 in cover 56 and are threaded into holes 74 in pump housing 54.

Referring to FIG. 2, pump housing 54 additionally includes a suction port or inlet 76 in fluid communication with the atmosphere, and discharge port or outlet 78 which extends through first spacer portion 62 and is in fluid communication with secondary air passage 80 (FIG. 1) which extends between and connects pump housing 54 and muffler 44 upstream of the catalyst element within muffler 44.

Referring additionally to FIG. 4, first impeller 82 is keyed to the upper end of crankshaft 26 for rotation therewith, and includes a pair of lobes 84 which are shaped as overlapping circles. Second impeller 86 includes hub portion 88 (FIGS. 2 and 3) fitted to the upper end of camshaft 32 for rotation therewith, and includes four lobes 90, each generally shaped as a V-shaped projection having curved surfaces. The number of lobes of first and second impellers 82 and 86 may vary as desired. Lobes 84 and 90 of first and second impellers 82 and 86, respectively, do not directly engage the interior of chambers 58 and 60 of pump housing 54 nor do lobes 84 and 90 directly engage one another. Rather, as shown in FIGS. 4-10, lobes 84 and 90 are disposed very closely adjacent the interior of chambers 58 and 60 of pump housing 54 and one another, as shown in FIGS. 4-10.

Referring to FIGS. 4-10, operation of secondary air pump 52 will be explained. Referring to FIG. 4, impellers 82 and 86 are shown in a first, arbitrary position in a pump cycle in which inlet 76 and outlet 78 are each substantially covered by portions of lobes 84 and 90 of first and second impellers 82 and 86. In FIGS. 5 and 6, first impeller 82 is rotated clockwise and second impeller 86 rotated clockwise such that the lobes 84 and 90 thereof progressively expose inlet 76 to define an expanding working space 92 proximate inlet 76 for drawing atmospheric air into the working space 92.

Concurrently, another working space 94 defined between lobes 84 and 90 is placed into fluid communication with outlet 78. If outlet 78 lacks a check valve, the air within working space 94 will be forced through outlet 78 as working space 94 contracts as shown in FIGS. 7-10, and the air will thence pass through passage 80 to muffler 44. Initially, the air within the contracting working space 94 may be held therewithin by back pressure in the exhaust passage, but the continued contraction of working space 94 as shown in FIGS. 7-10 will overcome such backpressure and force the air through outlet 78 and passage 80 into muffler 44 to combine with the exhaust stream. Also, during the contraction of working space 94 as shown in FIGS. 7-10, some slight compression of the air within working space 94 may occur. Alternatively, if greater compression of the air within working space 94 is desired, outlet 78 may include a check valve therein, which would open only when the air within working space 94 reaches a predetermined pressure.

In FIGS. 7-10, the working space 92 associated with inlet 76 continues to expand to further draw atmospheric air into working space 92. Eventually, working space 92 is divided into two working spaces 96 and 98 associated with first and second impellers 82 and 86, respectively. Working spaces 96 and 98 eventually join to form a working space 94 as described above before the air therewithin in discharged through outlet 78.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

1. An internal combustion engine, comprising: an engine housing; first and second shafts rotatably supported by said engine housing; and an air pump, comprising: a pump housing; an inlet in fluid communication with the atmosphere; an outlet in fluid communication with an exhaust system of said engine; first and second impellers disposed within said pump housing and driven respectively by said first and second shafts, said impellers cooperating with one another and with said pump housing to define a plurality of moving working spaces which convey air from said inlet to said outlet upon rotation of said first and second impellers.
 2. The internal combustion engine of claim 1, wherein said first and second impellers each include a plurality of lobes in meshing cooperation with one another.
 3. The internal combustion engine of claim 2, wherein said first shaft drives said second shaft at one-half the speed of said first shaft, and said second impeller includes twice the number of said lobes as said first impeller.
 4. The internal combustion engine of claim 2, wherein said first shaft drives said second shaft at one-half the speed of said first shaft, and said first impeller includes two said lobes and said second impeller includes four said lobes, whereby four of said working spaces convey air from said inlet to said outlet for each rotation of said second shaft.
 5. The internal combustion engine of claim 1, wherein said first shaft is a crankshaft, said crankshaft in timed driving relationship with said second shaft.
 6. The internal combustion engine of claim 1, wherein said second shaft is a camshaft, said camshaft in timed driven relationship with said first shaft.
 7. The internal combustion engine of claim 1, wherein said pump housing is formed at least in part by said engine housing.
 8. The internal combustion engine of claim 1, wherein said exhaust system of said engine comprises: an exhaust passage in fluid communication with said air pump outlet; a catalyst element disposed within said exhaust passage downstream of said air pump outlet; and a muffler associated with said exhaust passage.
 9. The internal combustion engine of claim 1, further comprising a one-way valve associated with said air pump outlet.
 10. An internal combustion engine, comprising: an engine housing; a crankshaft rotatably supported by said engine housing; an additional shaft driven from said crankshaft and rotatably supported by said engine housing; an exhaust system including an exhaust passage and a catalyst element; and an air pump, comprising: a pump housing including an inlet in fluid communication with the atmosphere and an outlet in fluid communication with said exhaust passage at a location upstream of said catalyst element; and first and second impellers disposed within said pump housing and driven respectively by said crankshaft and said additional shaft, said impellers each including a plurality of lobes in meshing cooperation with one another to define moving working spaces which convey air from said inlet to said outlet upon rotation of said first and second impellers.
 11. The internal combustion engine of claim 10, wherein said additional shaft is a camshaft, said camshaft in timed driven relationship with said crankshaft.
 12. The internal combustion engine of claim 11, wherein said crankshaft drives said camshaft at one-half crankshaft speed, and said second impeller includes twice the number of said lobes as said first impeller.
 13. The internal combustion engine of claim 11, wherein said crankshaft drives said additional shaft at one-half crankshaft speed, and said first impeller includes two said lobes and said second impeller includes four said lobes, whereby four of said working spaces convey air from said inlet to said outlet for each rotation of said additional shaft.
 14. The internal combustion engine of claim 10, wherein said pump housing is formed at least in part by said engine housing.
 15. The internal combustion engine of claim 10, wherein said pump housing further comprising a one-way valve associated with said air pump outlet.
 16. An internal combustion engine, comprising: an engine housing; first and second shafts rotatably supported by said engine housing; and an air pump, comprising: a pump housing; an inlet in fluid communication with the atmosphere; an outlet in fluid communication with an exhaust system of said engine; and means within said pump housing for conveying air from said inlet to said outlet upon rotation of said first and second shafts.
 17. The internal combustion engine of claim 16, wherein said first shaft is a crankshaft and said second shaft is a camshaft, said camshaft in timed driven relationship with said crankshaft.
 18. The internal combustion engine of claim 16, wherein said exhaust system of said engine comprises: an exhaust passage in fluid communication with said air pump outlet; a catalyst element disposed within said exhaust passage downstream of said air pump outlet; and a muffler associated with said exhaust passage.
 19. The internal combustion engine of claim 16, further comprising a one-way valve associated with said air pump outlet. 